Did You Find Out? Get the Answer to the Riddle of E-News Issue No. 3, May 2019

2019-05-02

Pocket Money

How much money is in her saving account?

Laura wants to buy a smartphone and agrees to an installment payment plan. She has to pay 20 dollars in the first month, 30 dollars in the second month, 40 dollars in the thirdmonth, and a final payment of 90 dollars in the fourth month.

Once at home, Laura notes that she does not have enough money in her savings account to pay each installment. So, her father makes the following offer: before each payment is due, he will double the existing amount in her savings account. Laura is very happy with this offer and realizes that she will have exactly the same amount of money in her savings account at the end of the smartphone payment plan as she did when she started.

How much money does Laura have in her savings account?

Solution

The formulas below represent each installment:
x = amount in the savings account

Pepperl+Fuchs is a leading developer and manufacturer of electronic sensors and components for the global automation market. Continuous innovation, enduring quality, and steady growth have been the foundation of our success for more than 70 years. Pepperl+Fuchs employs 6,200 people worldwide and has manufacturing facilities in Germany, USA, Singapore, Hungary, Indonesia and Vietnam, most of them ISO 9001 certified.